uneven surface, pits

[Jake_Ding 0]

Hi guys,

I recently printed with white-color ABS and black-color PLA.  I found the parts always include pits and strings on the surface. You can see these defects in 'string and pits surface ABS. jpg' and 'string surface PLA. jpg'  attached below. This phenomenon is especially obvious when printing with white ABS. The weird thing is the pits and string only show up at certain areas instead of the whole surface. Like in 'string and pits surface ABS. jpg', defects only show up on one side of wall. They don't show up on the bottom surface or other walls. The same is true for 'string surface PLA. jpg' in which string-like dents only show up around the bottom section of the part.  

'string and pits surface ABS. jpg'

'string surface PLA. jpg'

 

I also attached the 'simulation for hinge joint.jpg' generated from CURA's layer view. I tried to find the hints from it. The place where the strings exist isn't the place where each printing loop initiates but I observed the nozzle will move faster around that place in simulation. I don't know why the simulation doesn't render the nozzle with constant moving speed. 

'simulation for hinge joint.jpg'

 

My second question is I got rough edges like in 'rough edge ABS.jpg' and 'rough edge ABS 2.jpg' attached. The serrated edges in 'rough edge ABS.jpg' show up around all thin-walled vertical edges. On the other side, there is only one rough edge in 'rough edge ABS 2.jpg' as you can see.

'rough edge ABS.jpg'

'rough edge ABS 2.jpg'

 

I also attached the 'simulation for end cap part.jpg' generated from CURA's layer view. I tried to find the hints from it.  I found the rough edge is the beginning place for each printing loop. 

'simulation for end cap part.jpg'

 

For the hardware, I attach the 'ABS enclosure.jpg' here. I only use this DIY enclosure for ABS printing. The printer is Anet A8. 

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'ABS enclosure.jpg'

 

For the CURA, the major settings for ABS are listed in 4 screenshots from 'CURA setting 1.jpg' to 'CURA setting 4.jpg'. Note that I always close the fan when printing with ABS. And I always printed multiple parts together to give enough ABS cooling time.  If I printed with PLA, the settings would be similar but I would lower the nozzle temperature down to 170 degree and bed temperature down to 60 degree with the fan turning on.

'CURA setting 1.jpg'

 

'CURA setting 2.jpg'

 

'CURA setting 3.jpg'

 

'CURA setting 4.jpg'

 

BTW, the ABS material has been dried out in oven under 175 Fahrenheit for 2.5 hours before printing. 

 

In conclusion, I can't find reasons why I got pits and strings on the surface. I also can't find the reason why I got rough edges on the parts. Could you give me some suggestions? 

 

Thanks,

Jake

 

Edited July 2, 2018 by Jake_Ding

[gr5 2,230]

You shouldn't have to ever dry out ABS or PLA.  Only nylon and pva.  I have 6 year ABS that still works great.  Not kept sealed up.

 

Enclosing the printer is good for ABS.  That was a good idea.

 

Your retraction distance is huge (6.5mm) and that could be the problem right there.  How far between your extruder and your hot end?  Isn't the extruder mounted on the print head?  I'm going to guess around 30mm.  You typically want about 5mm retraction per meter of distance between these 2 devices so you probably don't want to go over 1mm retraction.  UM printers have about a 1 meter tube between the feeder and the extruder so UM printers need typically 4.5mm retraction.  Not sure about your A8.

 

Make all the print speeds the same.  Don't have one at 15 and the other at 10.  Look at all the printing speeds and try setting them all to 20 if you want it to print slow and high quality.

 

And your travel speed you want to crank it up.  If it travels too slow you get more stringing, more pits and blobs.  150mm/sec is usually fine but 300mm/sec is reasonable as well.  I suspect the A8 can do 300mm/sec just fine.

 

 

 

 

[Jake_Ding 0]

Hi gr5,

Thanks a lot for your suggestions. I have set the retraction speed down to 1mm. The travel speed has been cranked up to 250mm/sec. I am gonna printed more this morning.

 

Some guys said the initial layer speed should be lower but you suggested to printed with constant speed. What's the reason behind it?

 

BTW, I saw many people suggested that the color dye will absorb water severely but the natural ABS is fine. I thought the little pits are caused by the evaporated moisture.

 

Thanks again.

[Jake_Ding 0]

Hi gr5,

You method works well for me! No strings,pits and the corner becomes smoother after smaller retraction and bigger travel speed. Could you tell me why does travel affect strings, blobs and pits? I curious about the reasons.

 

Thanks,

Jake